This invention relates in general to the field of subterranean exploration and, more particularly, to a single-blade underreamer.
Underreamers are generally used to form an enlarged cavity in a well bore extending through a subterranean formation. The cavity may then be used to collect resources for transport to the surface, as a sump for the collection of well bore formation cuttings and the like, or for other suitable subterranean exploration and resource production operations. Additionally, the cavity may be used in well bore drilling operations to provide an enlarged target for constructing multiple intersecting well bores.
One example of an underreamer includes a plurality of cutting blades pivotally coupled to a lower end of a drill pipe. Centrifugal forces caused by rotation of the drill pipe extends the cutting blades outwardly and diametrically opposed to each other. As the cutting blades extend outwardly, the centrifugal forces cause the cutting blades to contact the surrounding formation and cut through the formation. The drill pipe may be rotated until the cutting blades are disposed in a position substantially perpendicular to the drill pipe, at which time the drill pipe may be raised and/or lowered within the formation to form a cylindrical cavity within the formation.
Conventional underreamers, however, suffer several disadvantages. For example, the underreamer described above generally requires high rotational speeds to produce an adequate level of centrifugal force to cause the cutting blades to cut into the formation. An equipment failure occurring during high speed rotation of the above-described underreamer may cause serious harm to operators of the underreamer as well as damage and/or destruction of additional drilling equipment.
Additionally, density variations in the subsurface formation may cause each of the cutting blades to extend outwardly at different rates and/or different positions relative to the drill pipe. The varied positions of the cutting blades relative to the drill pipe may cause an out-of-balance condition of the underreamer, thereby creating undesired vibration and rotational characteristics during cavity formation, as well as an increased likelihood of equipment failure.
Accordingly, a need has arisen for an improved underreamer that provides increased control of subterranean cavity formation. The present invention provides a single-blade underreamer that addresses shortcomings of prior underreamers.
According to one embodiment of the present invention, a single-blade underreamer for forming a cavity within a well bore includes a housing rotatably disposed within the well bore, and a stabilizer coupled to the housing. The stabilizer is operable to stabilize the housing within the well bore during formation of the cavity. The underreamer also includes a single cutter pivotally coupled to the housing, and a piston slidably disposed within the housing and adapted to engage the cutter. A downwardly disposed force applied to the piston is operable to slide the piston relative to the housing and correspondingly extend the cutter outwardly relative to the housing from a retracted position to form the cavity during rotation of the housing.
According to another embodiment of the present invention, a method for forming a cavity within a well bore includes providing a single-blade underreamer within a well bore and applying a downwardly directed force to a piston of the underreamer. The piston is slidably disposed within a housing of the underreamer and is coupled to the cutter. The method also includes extending the cutter outwardly from a retracted position relative to the housing in response to movement of the piston relative to the housing from the applied force. The method further includes rotating the underreamer within the well bore and stabilizing the housing within the well bore during rotation of the underreamer.
The invention provides several technical advantages. For example, according to one embodiment of the present invention, a downwardly directed force is applied to a piston of the underreamer to cause outwardly directed movement of a cutting blade into a subterranean formation. The downwardly directed force applied to the piston may be varied to produce corresponding varying pressures on the formation by the cutting blade. Thus, the present invention may be used to accommodate a variety of formation densities and compositions. Additionally, decreased rotational speeds of the underreamer may be used to form the cavity, thereby substantially reducing or eliminating hazards associated with high speed rotating mechanisms.
Another technical advantage of the present invention includes substantially reducing or eliminating out-of-balance conditions resulting from rotation of the underreamer within a well bore. For example, according to one embodiment of the present invention, a single cutter is used to form the cavity within the formation, and a stabilizer is provided to substantially maintain the underreamer concentrically disposed within the well bore during cavity formation. Thus, out-of-balance conditions caused by varying positions of multiple cutting blades is substantially reduced or eliminated.
Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions, and claims.